Many organisms obtain critical information from the environment through olfactory signals. For instance, chemical signals are used for food localization, species identification, and mate recognition. Thus, the ability to perceive and respond to these signals is essential for an organism's survival and reproduction. The ultimate goal of the proposed research is to understand the genetic basis for variation in behavior in natural populations as it relates to chemical communication. The specific aims of this project are: (1) To characterize smell impaired (smi) loci in co-isotonic lines of D, melanogaster, and (2) To investigate how molecular variation in these loci contributes to variation in odor-guide behavior in a natural population. These studies will provide for the first time information about the effect of single nucleotide polymorphism's in defined genes on odor-guide behavior in natural population.